Structure of the magnetopause current layer at the subsolar point

Abstract

A one‐dimensional electromagnetic particle simulation model developed for the magnetopause current layer between the shocked solar wind and the dipole magnetic field at the subsolar point has been extended to include the interplanetary magnetic field (IMF) in the solar wind. Interaction of the solar wind with the vacuum dipole field as well as the dipole field filled with a low‐density magnetospheric plasma are studied. It is found that the width and the structure of the magnetopause current layer differ markedly depending on the direction of the IMF. When the IMF is pointing southward, the current layer between the solar wind and the dipole field is narrow, and the magnetic field has a single ramp structure caused by the reflection of the solar wind at that point. The current layer becomes several times wider and the magnetic field develops a multiple ramp structure when the IMF is northward. This broadening of the current layer is caused by the multiple reflection of the solar wind by the magnetic field. For the northward IMF the magnetic field does not change its sign across the current layer, so that the E × B drift of the solar wind electrons remains the same direction, while for the southward IMF it reverses the sign. This results in a single reflection of the solar wind for the southward IMF and multiple reflections for the northward IMF. When a low‐density magnetospheric plasma is present in the dipole magnetic field, a small fraction of the solar wind ions are found to penetrate into the dipole magnetic field beyond the reflection point of the solar wind electrons. The width of the ion current layer is of the order of the solar wind ion gyroradius; however, the current associated with the ions remains much smaller than the electron current so long as the density of the magnetospheric plasma is much smaller than the density of the solar wind. Comparisons of our simulation results with the recent spacecraft data of the magnetopause crossing near the subsolar point are provided.